The gradual deterioration, and eventual failure, of electrical cables, such as those used in underground residential distribution circuits (URD), is well known. Failure of such cables, which generally comprise a stranded conductor surrounded by a semi-conducting conductor shield, a polymeric insulation jacket, and an insulation shield, is primarily attributed to high electrical fields within the insulation jacket as well as long term exposure thereof to environmental moisture. Since replacing an underground cable is costly, a cable which has either actually failed, or is likely to do so in the near term based on statistical data, is often treated (rejuvenated) to restore the dielectric integrity of its insulation, thereby extending its useful life in a cost-effective manner. A typical method for treating such an in-service cable comprises introducing a tree retardant fluid into the void space (interstitial void volume) associated with the strand conductor geometry. This fluid is generally selected from a particular class of aromatic alkoxysilanes which can polymerize within the cable's interstitial void volume as well as within the insulation by reacting with adventitious water (see, for example, U.S. Pat. Nos. 4,766,011, 5,372,840 and 5,372,841). Such a method (herein referred to as a “low-pressure” restorative method) typically leaves a fluid reservoir pressurized at no more than about 30 psig (pounds per square inch gage) connected to the cable for a 60 to 90 day “soak period” to allow the fluid to penetrate (i.e., diffuse into) the cable insulation and thereby restore the dielectric properties.
Those skilled in the art of cable restoration currently have limited ability to predict the efficacy of one of the above low-pressure restorative methods in their quest for improved fluid compositions and optimized parameters. Moreover, this assessment of efficacy is time-consuming and generally limited to results on a particular cable/fluid combination operating under relatively specific conditions. For example, a current procedure utilized in the art to determine the performance of a fluid (or fluid mixture) requires that each candidate fluid is injected into a laboratory cable which is then subjected to an expensive and multi-month accelerated aging regimen at a single temperature, whereupon it is sacrificed in an AC breakdown (ACBD) or impulse breakdown test and also subjected to analysis of the concentration profile of the fluid's components. Unfortunately, this accelerated aging method does not address the impact of real world dynamic cable temperature variation and it has been shown to result in errors in the range of an order of magnitude when used to predict actual cable ACBD field performance. (See Bertini, “Accelerated Aging of Rejuvenated Cables—Part I”, IEEE/PES/ICC Apr. 19, 2005 and Bertini, “Accelerated Aging of Rejuvenated Cables—Part II”, IEEE/PES/ICC Nov. 1, 2006.)